Como saber qual os componentes que existe no form ?

use a propriedade components do form assim:

****
for i:= 0 to pred(form.componentcount) do
if form.components[i].classname = ´tedit´ then
(form.components[i] as tedit).text := ´sou um edit´;
****

até

procedure InserirComponentes(Owner:TComponent)
begin
ListBox1.items.add(Owner.Name);
for X := 0 to pred(Owner.ComponentCount) do
InserirComponentes(Owner.Components[X]);
end;

procedure TForm1.Button1Click(Sender:TObject);
begin
ListBox1.clear;
InserirComponentes(Self);
end;